This invention relates to a raster output scanner interface, and more particularly to an interface providing subpixel spot size and addressability.
In a typical raster output scanner (ROS), a light source, such as a laser diode or a helium-neon laser, emits a light beam that is modulated according to a video signal. The light beam is directed through conditioning optics onto the reflective facets of a rotating polygon. The polygon, typically rotating at a rate in the 3 to 23 thousand revolutions per minute range, then scans the beam through more conditioning optics and images the laser spot across the full process width of a photosensitive image plane, in the fast scan direction. Meanwhile, the image plane moves in the slow scan direction, approximately parallel to the fast scan direction, in synchronization with the ROS so that successive passes of the laser spot across the width of the image plane produce successive scan lines.
On the image plane there are imaged various primitives, including dots, lines and arcs, that constitute text characters and graphics. An important portion of the primitives are edges. Irregularities in edges between successive scan lines are readily perceived.
One technique to smooth edges is to simply image the primitives at a finer resolution. To achieve finer resolution (e.g., 600 spi), the ROS would need to be redesigned to increase the input data rate to accept the data needed to define the higher resolution. To image the increased data rate would require either increasing the speed of rotation of the polygon or the number of polygon facets, or some combination of these two approaches.
In general, the above approaches have proven adequate. These approaches, however, suffer the drawback of increased complexity and cost. Moreover, for high speed imaging (e.g., 120 ppm), the system clock rate needed to input and process the necessary image data becomes prohibitively fast, requiring expensive components to respond to the system clock, as well as careful layout to avoid noise problems and electromagnetic interference.